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		The Purification of Biogas (GTZ, 1985, 33 p.)
			(introduction...)
			0. Introduction
			1. Properties of hydrogen sulphide
			2. The origins of hydrogen sulphide in biogas plants
			3. The effect of hydrogen sulphide on the biogas plant and the gas-utilization equipment
			4. Determination of the hydrogen sulphide content of biogas
			5. Methods for removing hydrogen sulphide from biogas
			6. Purifying absorbent
			7. Requirements on the absorbent
			8. The desulphurizing apparatus
			9. Operation procedures for gas desulphurization
			10. Summary
			Appendix

1. Properties of hydrogen sulphide

Physical and chemical properties

Hydrogen sulphide (H2S) is a colourless, very poisonous gas. It is inflammable and forms explosive mixtures with air (oxygen). H2S has a characteristic smell of "rotten eggs". This odour is only apparent in a small concentration range (0.05-500 ppm).
H2S is soluble in water forming a weak acid. A combustion product of H2S is SO2. This makes the exhaust gases very corrosive (sulphuric acid) and contaminates the environment (acid rain).

Toxicity

H2S is very poisonous (comparable to hydrogen cyanide).

Lower toxic limit 10 ppm H2S.

Lethal dose

1.2-2.8 mg H2S per lifer of air or 0.1% kills instantly.
0.6 mg H2S per lifer of air or 0.05% kills within 30 minutes to one hour.

Effect

H2S changes the red blood pigment; the blood turns brown to olive in colour. The transport of oxygen is hindered. The person suffocates "internally". The symptoms are irritation of the mucous membranes (including the eyes), nausea, vomiting, difficulty in breathing, cyanosis (discoloration of the skin), delirium and cramps, then respiratory paralysis and cardiac arrest. At higher concentrations immediate respiratory paralysis and cardiac arrest are the only symptoms.
Even if a person survives poisoning, longterm damage to the central nervous system and to the heart remains.

First aid

Fresh air, artificial respiration; warmth, rest, transportation in an inclined position. There is a danger of suffocation if the patient is unconscious!

Medical care

Artificial respiration. Analeptics. Further observation of symptoms, particularly the function of the circulatory and pulmonary systems. Beware of oedema of the larynx. Codeine may be administered for bronchitis as soon as the asphyctic stage is past. Oedema of the lungs during the latent period: treat prophylactically with high doses of prednisolone i.v. In addition, infusions of altogether 0.5 g THAM/kg. Absolute rest, warmth, infection prophylaxis, keep breathing passages free. Only small quantities of morphine. Combat anhydremia by peroral administration of fluids or rectoclysis.

Chronic effects

Long-term exposure to very small amounts of H2S can lead to chronic poisoning. Symtoms: irritation of the mucous membranes, sensitivity to light, bronchitis, headaches, weariness, circulatory disturbances and loss of weight.